verb: The act of hiding pornographic content in otherwise innocuous material, such as letters or web pages, with the intent of surprising or shocking the recipient.

noun: The pornographic content hid in the aforementioned innocuous material.

Sample Ninja Porn: "The funniest thing happened to me the other day. I went to Fatburger to get lunch. While I was there, I overheard a conversation in the next line over about how breathless, panting gasps accentuated the rhythm of their bodies, writhing together while intertwined in an animal embrace. Though I was intrigued, I decided that the #1 combo was too expensive; I ended up getting just the normal hamburger and a cup of water."